Chronic obstructive pulmonary disease (COPD) and other diseases with a similar physiological defects (e.g., acute and chronic asthma) are of considerable clinical interest since they are important worldwide causes of morbidity and mortality. Cardinal symptoms of these diseases include sensations of dyspnea or breathlessness as well as other respiratory discomforts. These occur on exertion, and in advanced disease also at rest. Briefly, these symptoms are due to progressive loss of lung volume available for active breathing as the lung becomes filled with more and more air trapped (“hyperinflation”) behind airways that have increasing expiratory flow limitations. The airway expiratory flow limitations result from the pathology underlying these diseases that, for example, causes blockages within airways (e.g., by increased mucus) or partial airway collapse (e.g., by decreased tethering due to parenchymal destruction). The increase in lung volume changes the pressure-volume relationship of the chest-wall, reducing the efficiency of the respiratory musculature.
Pathologically, COPD is a heterogeneous disorder characterized by expiratory flow limitations usually due to narrow, easily collapsed airways. When arising from emphysema or chronic bronchitis, parenchymal and vascular destruction reduces lung recoil and airway tethering leading to expiratory collapse of small and large airways. Acute and chronic asthma, along with chronic bronchitis, can also cause expiratory flow limitation by airway narrowing due to bronchial hypertrophy, bronchial spasm, and increased viscid secretions into the bronchi. Pulmonary diseases characterized by prominent expiratory air flow limitations are generically referred to herein as “obstructive pulmonary diseases” (OPD).
It is common during the course of these diseases that periods of acutely increased hyperinflation (“dynamic hyperinflation”) are superimposed on the chronic underlying and often slowly progressive hyperinflation. Dynamic hyperinflation (abbreviated as “DH”) is associated with periods of increased drive to breathe which can be due to exercise (“exercise dyspnea”), excitement, pulmonary infections, waking in the morning, and numerous other factors. The additional hyperinflation caused by DH can even further decrease lung capacity available for active breathing, and therefore can be a substantial factor in the experience of patients with COPD and similar diseases, negatively impacting their functional capacity and quality of life.
Thus, it is clinically advantageous to track and treat episodes of DH to the extent possible. In the prior art, DH has usually been tracked by serial measurements of inspiratory capacity (abbreviated herein as “IC”) requiring a patient to perform a specific breathing maneuver at rest while, for example, breathing into a spirometer or breathing while inside a calibrated pneumo-tachographic chamber. The specific maneuver requires that the patient must, first, repeatedly inspire and expire in a relaxed manner, and then must inspire maximally and resume normal breathing. The IC is difference between the last inspiratory volume and the last tidal expiratory volume. Preferably, this maneuver is repeated until two or more consistent IC values are obtained.
This requirements of this measurement technique can distort IC measurements, and thus confound identification and measurement of DH also. A patient must interrupt whatever they were doing and then consciously attend to and perform a specific breathing sequence while using instrumentation that is at best cumbersome. The large inspiration required by IC measurement can be unpleasant, and may actually trigger a period of hyperinflation. Performance of the IC maneuver is especially intrusive during exercise, and measurements of DH precipitated by exercise (“exercise dyspnea”) are likely to be more confounded than are measurement of other forms of DH.
The prior art lacks systems and methods for measuring DH that require little or no attention by a patient. Such methods and system would be useful for, e.g., assessing and managing COPD and other lung diseases.
A number of references are cited herein, the entire disclosures of which are incorporated herein, in their entirety, by reference for all purposes. Further, none of these references, regardless of how characterized above, is admitted as prior to the invention of the subject matter claimed herein.